Platinum catalysts and bimetallic catalytic composites of platinum and other metals, such as tin, on a refractory support are well known. See, e.g., U.S. Pat. No. 3,531,543 (Clippinger et al.), U.S. Pat. No. 3,745,112 (Rausch), U.S. Pat. No. 3,840,475 (Davis), U.S. Pat. No. 3,864,241 (Rausch), and U.S. Pat. No. 3,883,419 (Itoh et al.). The platinum, which is typically present in amounts of 0.1 to 5% by weight, is an active catalyst for hydrogenation or dehydrogenation and dehydrocyclization of vaporized hydrocarbons under appropriate process conditions; and deposited on suitable porous supports, platinum also is known to catalyze isomerization and cracking. Bimetallic catalysts, in which a second metal such as tin, cobalt, nickel, iron, copper, palladium, germanium, iridium, rhodium, rhenium etc. is used to stabilize or enhance the platinum activity, have been developed in order to prevent agglomeration of the platinum, facilitate regeneration and enhance selectivity, or, as in the case of rhenium, to reduce the amount of expensive platinum metal required to produce an active hydrocarbon conversion catalyst.
Bimetallic catalytic composites comprising a combination of catalytically effective amounts of platinum, a second metal (particularly tin) and a halogen component on a porous carrier material have been developed which exhibit good activity, selectivity and stability when utilized in hydrocarbon reforming processes.
Reforming of hydrocarbon naphtha streams is a particularly important hydrocarbon refining process in which high octane hydrocarbon blending components for gasoline or for chemical processing feedstocks are obtained from low octane petroleum fractions. Catalytic reforming of naphthas has been performed with a wide range of platinum-containing catalysts in fixed and moving bed processes.
In the manufacture of reforming catalysts, many factors are considered with a view to optimizing the volume of high octane materials produced using a particular catalyst. For example, the amounts and types of metals combined with the platinum may be varied, as well as the chemical nature of the bimetallic combination, that is, whether the deposited metals are in a positive oxidation state, elemental, or form a solid solution (alloy). See, e.g., U.S. Pat. No. 4,016,068 (Rausch) and U.S. Pat. No. 3,759,823 (Davies et al.).
In addition to varying the amount of platinum or the types and content of any other metallic components, the physical properties of the catalyst support may also be varied with a view to altering the overall properties of the catalytic composite. See, e.g., U.S. Pat. No. 4,703,031 (Unmuth et al.).
Applicants have found that formation of an improved catalytic composite comprising a combination of elemental platinum, or elemental platinum and a second metal in elemental form selected from tin, cobalt, nickel, iron, copper, palladium, germanium, iridium, rhodium or rhenium, and a halogen component, uniformly deposited on a unique porous, high surface area, spherical alumina carrier such that the platinum and tin components are uniformly dispersed throughout the porous carrier support material, provides an improved reforming catalyst having activity, selectivity and stability characteristics so that the average yields of C.sub.5+ reformate over a cycle are increased and the operation of the catalyst at high severity conditions is improved over catalytic composites prepared according to the prior art. Catalytic composites prepared as described herein, therefore, represent an advance in the art by enabling more efficient naphtha reforming processes and producing higher quality gasolines and chemical processing feedstocks.